Classical Reaction Barriers in DFT: An Adiabatic-Connection Perspective.

Classical reaction barriers in density-functional theory are considered from the perspective of the density-fixed adiabatic connection. A 'reaction adiabatic-connection integrand', , is introduced, where λ is the electron-electron interaction strength, for which equals the barrier, meaning the barrier can be easily visualized as the area under a plot of vs λ. For five chemical reactions, plots of reference , calculated from Lieb maximizations at the coupled-cluster level of theory, are compared with approximate , calculated from common exchange-correlation functionals using coordinate scaling, for coupled-cluster densities.

Symmetry and reactivity of π-systems in electric and magnetic fields: a perspective from conceptual DFT.

The extension of conceptual density-functional theory (conceptual DFT) to include external electromagnetic fields in chemical systems is utilised to investigate the effects of strong magnetic fields on the electronic charge distribution and its consequences on the reactivity of π-systems. Formaldehyde, HCO, is considered as a prototypical example and current-density-functional theory (current-DFT) calculations are used to evaluate the electric dipole moment together with two principal local conceptual DFT descriptors, the electron density and the Fukui functions, which provide insight into how HCO behaves chemically in a magnetic field. In particular, the symmetry properties of these quantities are analysed on the basis of group, representation, and corepresentation theories using a recently developed automatic program for symbolic symmetry analysis, QSYM.

QSym: A Quantum Symbolic Symmetry Analysis Program for Electronic Structure.

Symmetry provides a powerful machinery to classify, interpret, and understand quantum-mechanical theories and results. However, most contemporary quantum chemistry packages lack the ability to handle degeneracy and symmetry breaking effects, especially in non-Abelian groups, and they are not able to characterize symmetry in the presence of external magnetic or electric fields. In this article, a program written in Rust entitled QSym that makes use of group and representation theories to provide symmetry analysis for a wide range of quantum-chemical calculations is introduced.

Software for the frontiers of quantum chemistry: An overview of developments in the Q-Chem 5 package.

This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange-correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods.

Symmetry in Multiple Self-Consistent-Field Solutions of Transition-Metal Complexes.

We use a method based on metadynamics to locate multiple low-energy Unrestricted Hartree-Fock (UHF) self-consistent-field (SCF) solutions of two model octahedral d and d transition-metal complexes, [MF] (M = Ti, V). By giving a group-theoretical definition of symmetry breaking, we classify these solutions in the framework of representation theory and observe that a number of them break spin or spatial symmetry, if not both. These solutions seem unphysical at first, but we show that they can be used as bases for Non-Orthogonal Configuration Interaction (NOCI) to yield multideterminantal wave functions that have the right symmetry to be assigned to electronic terms.

MR arthrography: impact of steroids, local anesthetics, and iodinated contrast material on gadolinium signal intensity in phantoms at 1.5 and 3.0 T.

Purpose: To determine if gadolinium signal intensity at direct magnetic resonance (MR) arthrography is affected by the addition of steroids, anesthetics, or iodinated contrast material.

Materials And Methods: This study did not require approval by the institutional review board because no patients or patient data were involved. An in vitro study was performed to evaluate various concentrations of three gadolinium contrast agents (gadopentetate dimeglumine, gadobenate dimeglumine, and gadofosveset trisodium) diluted in either saline or iodinated contrast material (50% and full-strength iohexol 300).

Shoulder MR arthrography: intraarticular anesthetic reduces periprocedural pain and major motion artifacts but does not decrease imaging time.

Purpose: To prospectively determine whether the addition of an intraarticular anesthetic to the magnetic resonance (MR) arthrography solution has an effect on periprocedural pain, motion artifacts, and imaging time.

Materials And Methods: This study was approved by the institutional review board, and written informed consent was obtained from all patients. From September 2009 to March 2010, 127 patients, most imaged for shoulder pain, were randomized into two groups.

An ovary with a twist: a case of interesting sonographic findings of ovarian torsion.

An otherwise healthy young woman presented to the Emergency Department with abdominal pain. Multiple diagnoses were considered, as must be in cases of women with lower quadrant abdominal pain. Rapid identification of an abnormally enlarged ovary in close proximity to the opposite ovary on pelvic ultrasonography suggested the diagnosis of ovarian torsion.